1. Field of the Invention
This invention relates to well cementing tools and more particularly to pipe wipers such as cementing plugs and pump-down plugs and to cups for use on such pipe wipers.
In cementing pipestrings such as casings and liners in well bores so that such pipestrings are firmly and sealingly bonded to the earth, cement slurry is pumped down such pipestring and followed by water until the slurry rises to the desired level in the well bore about the exterior of the pipestring, and then the slurry is allowed to stand until it hardens.
In some cases, a wiper plug is placed in the pipestring behind the cement slurry and ahead of the water to separate the two and to assure that all cement slurry is wiped from the inner wall of the pipestring.
In some wells, the pipestring which reaches the greatest depth does not extend to the earth's surface as do the other pipestrings. This lowermost pipestring is called a "liner," and its upper end is disposed within and suspended from the lower portion of the next outer pipestring. The liner usually has a liner hanger mechanism attached at its upper end, and this hanger is suspended from a liner hanger running tool attached to a running-in string, usually drill pipe, by which the liner is lowered into the well. Generally, in such cases, a liner wiper plug is releasably attached to the lower end of the liner hanger running tool within the liner, and this wiper plug has a longitudinal flow passage through it so that cement slurry and other fluids may be circulated downwards through the liner and upwards about its exterior. When the last of the cement slurry has been forced into the running-in string at the surface, a pumpdown wiper plug is launched into the flow stream and is pumped down the well ahead of water or other medium.
The pumpdown wiper plug wipes the inner wall of the running-in string free of cement slurry, and when it reaches the liner hanger running tool, it will lodge in the liner wiping plug, plugging its bore. This causes fluid pressure to increase above the wiper plugs, and when this pressure increases to a predetermined value, the liner wiper plug is released from the liner hanger. This rise and drop of fluid pressure as the pumpdown plug engages the liner wiper plug and the liner wiper plug is released is observable at the surface and indicates to the operator that the tail end of the cement slurry has entered the upper end of the liner. The liner wiper with the pumpdown wiper plug lodged in and plugging its bore now is pumped downwards in the liner and wipes the inner wall of the liner free of cement slurry.
Downward movement of the liner wiper plug is generally limited by a landing receptacle or latch down collar in which a forward or nose portion of the liner wiper latches and seals. Of course, when the liner wiper plug engages the latch down collar, the pump pressure rises abruptly, thus indicating to the operator that the tail end of the cement slurry has reached the lower end of the liner and that the cement slurry is in place surrounding the liner. When this slurry sets, it will bond the liner to the wall of the earth borehole. Afterwards, the slight amount of cement plugging the liner's lower end can be drilled out if desired. Of course, the liner wiper plug and the pumpdown plug must be drilled up also in such case, and for this reason the rigid or metallic portions thereof are formed of a readily drillable material such as aluminum.
Pipe wipers or wiper plugs for use in well cementing operations and particularly those used in cementing liners in place, and more particularly the pumpdown wiper plugs used in liner cementing operations have been a problem on occasion because their cup-like lips were too easily turned wrong side outward as in cases where the pumpdown plug lodged in the running-in string on the way down, or lodged in the liner hanger running tool but above the liner wiper plug. Pumpdown plugs have been known to malfunction in the launching mechanism at the surface when, due to faulty assembly or faulty operation of the launcher, the wiper cups turned wrong side outward at such low pressure differentials as to go unnoticed, and instead of following the cement slurry down, the plug stayed in the launcher. Thus, the cement slurry could not be spotted or placed in the desired location. Such malfunctions are understandably costly and time-consuming, and cement is very unforgiving.
2. Description of the Prior Art
Pipe wipers, such as the pumpdown plugs and wiper plugs used in operations in which casing strings and liners are cemented in place in wells, have appeared in various forms and made of various materials. Many of these plugs and wipers have had external annular flanges or lips formed of a resilient material such as an elastomer, usually a synthetic rubber. The annular lips were usually slanted rearwardly and in many cases resembled cups.
Examples of such wiper plugs and pumpdown plugs and equipment used therewith for cementing pipe strings in wells are typically shown in the following U.S. Patents: Nos.
1,822,193 PA1 1,994,072 PA1 2,165,433 PA1 3,437,137 PA1 3,545,542 PA1 3,605,896 PA1 3,616,850 PA1 3,635,288 PA1 3,796,260 PA1 3,910,349 PA1 3,934,652 PA1 3,948,322
U.S. Pat. Nos. 3,910,349 and 3,934,652 to Chudleigh B. Cochran disclose apparatus and methods for cementing well liners. Wiper plugs and pumpdown plugs are shown in each of these two patents.
U.S. Pat. No. 3,437,137 to Lyle B Scott shows wiper plugs for use in the process of cementing casing in wells.
U.S. Pat. No. 3,605,896 to Lee E. Perkins shows plugs used in the process of cementing pipestrings in wells, and in FIG. 4 of this patent there is illustrated a pumpdown plug which is the nearest prior art found relating to the present invention.
None of the prior patents found show or teach pipe wipers or cups having radially disposed webs for strengthening the flange of such devices to enable them to better resist forces tending to turn them wrong side outward.